1. Field of the Invention
The invention relates to a method for the photolithographic production of structures in the submicron range.
2. Description of Related Art
In the photolithographic production of structures, TSI single-layer resists (TSI=top surface imaging) which can be dry-developed exhibit the advantages of two-layer resists (with wet development of the top resist and dry development of the bottom resist), such as suppression of reflections and reduction of topography effects. Furthermore, they offer the additional advantage that only a single resist layer has to be applied to the substrate, generally a silicon wafer, and that wet development is eliminated. A detailed description of systems of the type stated is found in "Introduction to Microlithography," ACS Symposium Series 219 (1983), pages 287 to 350.
TSI resists are known both in the form of single-layer systems which work in positive manner, and in the form of single-layer systems which work in negative manner and can be dry-developed. In contrast to negative systems, positive TSI systems, because of their lower defect density, are much better suited for applications in the contact hole planes, which are very critical.
Single-layer systems which can be dry-developed function according to the following principle:
- application of the resist to a silicon wafer; PA1 - exposure, and, if necessary, heating, in order to produce a "latent" image; PA1 - treatment with a metallization agent, for example an organometal compound, where the resist, in the exposed areas (negative resists) or in the unexposed areas (positive resist), becomes resistant to dry development, especially in oxygen plasma; PA1 - dry development. PA1 1. Simple and line-compatible processing PA1 2. Great sensitivity PA1 3. High resistance to plasma development, i.e. ability to be developed without residue PA1 - EP-OS 0 136 130 PA1 - U.S. Pat. No. 4,551,418 PA1 - U.S. Pat. No. 4,613,398 PA1 - U.S. Pat. No. 4,657,845 PA1 - EP-OS 0 248 779 PA1 - EP-OS 0 281 182 and U.S. Pat. No. 4,921,778 PA1 - "Mat. Res. Soc. Symp. Proc.," Vol. 45 (1985), pages 197 to 202, as well as "IBM Tech. Discl. Bull.," Vol. 27, No. 4A (1984), page 2197 PA1 - a photoresist layer comprising a polymer containing carboxylic acid anhydride and carboxylic acid tert. butyl ester groups, a photoinitiator which releases an acid when exposed, and a suitable solvent is applied to a substrate, PA1 - the photoresist layer is dried, PA1 - the photoresist layer is exposed in an imagewise manner, PA1 - the exposed photoresist layer is subjected to temperature treatment, PA1 - the photoresist layer treated in this way is subjected to liquid silylation, and PA1 - the silylated photoresist layer is dry-developed in an anisotropic oxygen plasma, i.e. in a plasma containing oxygen,
This number of process steps is not supposed to be exceeded in production.
A high-resolution TSI system which is practical for production is supposed to satisfy the following requirements:
More process steps than the ones stated above mean a greater cost expenditure, where the additional costs can be caused by capital investments for additional equipment and/or reagents as well as by error sources due to the additional process steps, which result in a lower yield. PA2 The lower the sensitivity, the lower the throughput at the expensive steppers, and the greater the costs. A high sensitivity in the DUV range (DUV=deep UV), for example at 248 nm, is particularly important, since resolution increases with a decreasing wavelength. PA2 A high resistance of the areas treated with the metallization agent is important for a high degree of freedom in the process in dry developing, while the ability to be developed without residue is important for yield. In order to achieve the ability to be developed without residue, a two-stage etch process is sometimes necessary, with developing taking place first in a plasma containing halogen, and then in an oxygen plasma. This in turn presupposes a very great etch stability of the layer areas treated with the metallization agent. PA2 With the process described, positive and negative structures can be produced, with UV light or with electron beams. The need for a special apparatus (for vacuum) as well as the requirement for metallization with corrosive or toxic gases, such as B.sub.2 H.sub.6, SiCl.sub.4 and TiCl.sub.4, which are not very well suited for production, is a disadvantage. PA2 A method for the production of a negative resist structure is described, in which a base polymer which contains a cationic photoinitiator, especially a triaryl sulfonium salt or a trihalogenated methyl triazine, is used. After exposure, the resist layer is then treated with a monomer which can be cationically polymerized, such as epoxy siloxane and epoxy silane, or styrene silyl ether (in the gas phase or in solution), in order to form a polymer film, which protects the exposed areas during the subsequent plasma etch process. PA2 Systems which work positively and negatively are described, where the permeability of the resist relative to the metallization agent is changed by exposure. Disadvantages of this system in the positive mode are a low DUV sensitivity (50 to 300 mJ/cm.sup.2) and the requirement of silylation with hexamethyl cyclotrisilazane in o-xylene at 65.degree. C., for which a special apparatus is required, and thus there is little production line compatibility. PA2 A method is described, which is based on the principle of chemical amplification and demonstrates high DUV sensitivity (approximately 6 mJ/cm.sup.2). However, two additional process steps are required here, namely a metal-free treatment with methyl isocyanate, specifically in the vacuum oven, as well as flood exposure. PA2 Although the method described involves few process steps, a special apparatus for gas phase silylation at an elevated temperature is required. In addition, the system of polyvinyl phenol and bisazide used does not have great DUV sensitivity. The same also applies for a system known from EP-OS 0 318 956. PA2 Although the systems described demonstrate good DUV sensitivity, they have the disadvantage that a special apparatus for silylation from the gas phase at an elevated temperature is required. Furthermore, the silylated areas demonstrate only moderate etch resistance, due to the embedding of monomer silicon fragments, such as Si(CH.sub.3).sub.3 groups (see also in this regard: "Microelectronic Engineering," Vol. 3 (1985), pages 279 to 291). PA2 The method described is based on the decarboxylation of homopolymers or copolymers of (meth)acrylic acid, and possibly of its anhydride, by high-energy radiation and silylation of the unexposed areas from the gas phase. The disadvantages consist of the gas phase silylation (requirement of special equipment), the relatively low etch resistance in the oxygen plasma (due to silylation with hexamethyl disilazane) and the lack of DUV sensitivity of a decarboxylation reaction of the type stated.
In order to solve the problem of a low DUV sensitivity of photoresists, resist systems were developed, the base polymers of which demonstrate tert. butyl ester or tert. butoxycarbonyloxy groups (see in this regard U.S. Pat. Nos. 4,491,628 and 4,552,833). When exposed in the presence of a strong acid forming agent, for example a so-called Crivello salt, carboxyl or phenolic OH groups are formed, with a single proton splitting off several groups, according to the principle of so-called "chemical amplification" (see in this regard, for example "J. Electrochem. Soc.," Vol. 136 (1989), pages 1453 to 1456).
Several TSI systems are already known, but none of them completely satisfies the requirements stated above:
Furthermore, a structuring method with dry development has already been proposed, which yields positive images, where subsemimicron structures can be produced, using normal apparatus (see: U.S. patent application Ser. No. 682,142 dated Apr. 8, 1991, now U.S. Pat. No. 5,229,258 issued Jul. 29, 1993). However, this method involves two additional process steps, namely treatment of the exposed photoresist layer with a polyfunctional organic compound, especially a polyamine, and flood exposure.
In addition, a method has already been proposed, with which high-resolution negative resist structures with steep slopes can be obtained, using a resist system that can be dry-developed (see: U.S. patent application Ser. No. 692,364 dated Apr. 26, 1991, now U.S. Pat. No. 5,262,283 issued Nov. 16, 1993). The resist system in this case is based on a polymer which has anhydride groups as well as blocked imide or phenolic hydroxyl groups, and an acid forming agent. This system, which functions according to the principle of chemical amplification, does have a greater sensitivity than comparable known systems (see: EP-OS 0 394 740), especially in the DUV spectrum (for example at an exposure of 248 nm), but still does not entirely fulfill the latest strict requirements of production. According to these, the sensitivity is supposed to be better than 20 mJ/cm.sup.2, measured with steppers with a KrF excimer laser as the light source (not with contact exposure devices with a Hg/Xe lamp, which simulate sensitivity which is better by a factor of at least 4).